Telephone-exchange system



5. B. WILLIAMS El AL TELEPHONE EXCHANGE SYSTEM Jan. 5 1926.

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Filed Jan. 25, 1925 Jan. 5 1926.

s. B. WILLIAMS ET AL TELEPHONE EXCHANGE SYSTEM rim Jan. 25, 1925 sh" Jan. 5 1926. 1,568,305

5. B. WILLIAMS ET AL TELEPHONE EXCHANGE SYSTEM Filed Jan. 25, 1925 8 Sheets-Sheet 5 Jan. s, 1926. 1,568,306

S. B. WILLIAMS AL TELEPHONE EXCHANGE SYSTEM Filed Jan. 23, 1925 s Sheets-Sheet 4.

hue/7mm: Jayme/5 VV/J/K/J/WG J. aw /7 & Af/j/ Jan. 5,1926. 1,568,306

S. B. WILLIAMS ET AL TELEPHONE EXCHANGE SYSTEM Fil 25, 1925 8 Sheets-Sh t 5 Jan. 5, 1926. 1,568,306

S. B. WILLIAMS r AL TELEPHONE EXCHANGE SYSTEM Filed Jan. 23, 1925 8 sheetshsheet 6 S. B. WILLIAMS ET AL TELEPHCNE EXCHANGE SYSTEM- Jal 5 1926. 1,568,306

Fil 25' 92 8 Sheets-Sheet 7 d/Af 6/5150 y Y fly Jan. 5 1926. 1,568,306

S. B. WILLIAMS ET AL TELEPHONE EXCHANGE SYSTEM Filed Jan. 23, 1925 8 Sheets-Sheet 8 five/7mm: Jam/e/E VV////d/776 Patented Jan. 5, 1926.

UNITED STATES PATENT OFFICE.

SAMUEL B. WILLIAMS, OF BROOKLYN, NEW YORK, AND EARL S. GIBSON,

WOOD, NEW JERSEY, ASSIGNORS, BY MESNE ASSIGNMENTS, TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE V SYSTEM.

Application filed January 23, 1925.

To all ti /Will. it wmy concern:

lie it known that we, SAMUEL B. VVIL- LTAMS and EARL S- GIBSON, citizens of the United States of America, residing at Brooklyn, in the county of Kings and State of New York, and Ridgewood, in the county of Bergen and State of New Jersey, respectively, have invented certain new and useful Improvements in Telephone-EX- chan e Systems, of which the following is a ful clear, concise, and exact description.

This invention relates to telephone exchange systems and more especially to such systems wherein automatic switches and automatic switch controlling devices areemployed in the establishment and completion of conversational connections.

An object of the invention is toimprove the serviceability of telephone systems by providing an improved trunk testing mechanism whereby a simultaneous test may be made of a group of trunks which lead from a plurality of equivalent selector switches.

A feature of the invention relates to means for associating simultaneously all the test conductors of a marked group of trunks, leading to a private branch exchange, with a common testing equipment.

Another feature resides in the novel means for partially operating a plurality of selector switches wherein the trunks of a selected group originate and for completely operating only that switch wherein the first idle trunk of the group originates.

Other inherent features and advantages will become apparent after a consideration of the following description and from a consideration of the ap )ended claims.

The several figures oi the drawing when arranged in the manner indicated in Fig. 9 disclose a suflicient portion of a telephone system embodying the present invention, and in sufiicient detail to enable av complete undm'standing to be attained thereo'i' Referring to the drawings, Fig. l. represents in schematic form a. line switch and a. subscribers line terminating therein. This figure also shows a district selector switch anda sender selector snitch. In addition there is shown diagrammaticallyone of a number of trunks extending between the line switch and the CllStllQlj sw tch.

Fig, 2 in the upper central portion illustrates,

n of an .iee 'm na sele ts f Serial No. 4,147.

This figure also shows a called subscribers line and a number of groups of trunks which lead from the final switch to a private branch exchange. I

Fig. 42 shows another final selector switch similar to the switch of Fig.

Fig. 5 in the left hand portion schematically illustrates a registering and controlling senier. The central portion of this figure shows a sender connector, while the right hand portion illustrates schematically certain registers of the marker.

Fig. 6 shows certain controlling relays located in the marker.

Fig. '7 illustrates a number of connecting devices for associating the final selector switch with the marker and final translator.

Fig. 8 shows part of a final translator. The upper portion of this figure shows series of testing and blocking relays for testing and controlling the selection of an idle P. B. X. trunk. The remainder of this figure illustrates certain controlling relays of the final translator. L

Fig. 9 shows the manner in which the several sheets of the drawing. are to be arranged to produce a unitary circuit disclosure.

The invention is illustrated as applied to a telephone system of the general character disclosed in the eopenzling appli ot \Varren W. Carpenter, Serial No. Tit-1,1362, filed April 1, 1924. Reference may be had to said application for the details of construetion and operation of the various ,nmrlc ers and. corniccting. devices referred to here imitter,

The line switch lUQ. district switch 150. sender selector switch 2,60, incoming switch 200, final switches 300 and 400. may all be of the coordinate type such as described and claimed in U Spateet to J. N. Reynolds, 3 0. 402 star ed .s r sebei 2,. .3%

and further described in the U. S. patent to S. B. \Villiams, No. 1,517,331. Reference may be had to both of the above mentioned patents for a description of the construction andzthe-mode of operation of the various selector switches.

Inasmuch as the present invention is concerned principally with the manner of-testing for and seizing an idle trunk leading to a private branch exchange, the operation of the various selector switches and the connecting devices, as well as the manner in which these switches are controlled by the senders and markers will be described here iii-after in a comparatively general manner.

Detailed description.

Let it be assumed that the subscriber at station 101 has initiated a call with the purpose of communicating with a subscriber whose line is located in the private branch exchange represented diagrammatically by the rectangle 50. In response to the removal of the calling subscribers receiver from its switchhook, line 102 is extended by means of line switch to the district trunk 151. At the time trunk 151 is seized, sender selector switch 160 is actuated, resulting in the association of an idle registering and controlling sender 500 with trunk 151. In response to the dialing of the office code by the calling subscriber the district switch is selectively operated to seize a trunk such as trunk 152 which leads to the proper group of incoming switches. Sub sequently to the seizure of trunk 152, the sender connector 560 is actuated, resulting in the association of an idle incoming marker, or switch controlling mechanism, with the incoming sender 500. This marker comprises a set of register. relays for receiving the numerical designationsof wanted lines, aplurality of controllingrelays and sets of testing relays. Subsequently to the operation of connector 560 the numerical record is transferred from the registers of sender 500 to corresponding registers in the marker. Four of the marker registers are represented diagrammatically, namely, the units register 510, tens register 520, hundredsregister 530 and thousands register 5&0. At the time connector 560 is operated conductor 551 is grounded in the sender, resulting in the operation of relay 619. Relay 619 is a ground control relay and supplies ground for operatingand locking various relays in the marker. With the complete record transferred to registers 510, 520, etc., a circuit ,isclosed from ground through the left contacts of relay 619, conductor 667, through the hundreds register to battery, through the "winding of relay 517. Thenext step in the sequence of operations IS the association ofanidle final translator *Withthe incoming -inarker of Figs. 5 and 6. The selection .of this trans lator being determined by the combined setting of the thousands and hundreds regis ters 5&0 and 530 respectively,asdescribed in the-application oflV. V. Carpenter Serial No. 703,362. Assuming the translator represented in Fig. 8 to be idle at this time, a circuit is completed from battery, through the left outer contacts of relay 619, conductor 666, through thousands register 540, conductor 561, contacts of relay 517, conductor 562, right winding of relay 801, to ground at the back contacts of relay 802. Relay 801 looks through its left winding in series with the winding of relay802. Relay 802 operates'by means of this locking circuit and prevents a second marker from seizing thistrauslator. At this time also the record of the incoming frame involved, which has been previously registered in the sender 500 causes relay617 to be energized. For a detailed description of the manner in which the aforemention operations are effected, reference may be had to the application of W. V. Carpenter, Serial No. 703,362, referred to hereinbefore.

Vith relays 801 and 802 energized ground is extended through front contacts of these 'relays, thence to battery through the winding of multi-contact relay 803; also by means of parallel circuits through the windings of multi contaet relays 701 and 201. Relays 701 and 803 associate the marker with the final translator. The ground which was effective in operating relay 803 is also extended through the inner front contacts of relay 801, thence to batterv through the winding of relay 618 which operates'and locks to ground at the contacts ofrelay 619. In the manner described in detail in the Carpenter application, Serial No. 703,362, referred to above, relays 617 and 618 cooperate to cause the actuation ofthe incoming frame connector 210 resulting in the operation of vertical magnet 215. At this time also the multi-contact relay 208 is operated. The frame connector 210 associates the horizontal operating and testing conductors of switch 200 with the right hand-windings of the test relays 202,

203, 201-, etc. The left hand windings of these test relays are associated by means of relays 201 and 208 with the sleeve CO11- duct-ors of the proper group of trunks to which relay 208 is individual and including trunk 261. If either a link or a. trunk is busy the test conductor thereof is grounded causing the corresponding test relay to op- "erate and look through its left winding.

Intheananner described in detail in the applicationof VJJVV. Carpenteiy'Serial No. 703,362, referred to above, the setting of the hundreds register 530 causes ground to be connected through the left middle contacts their); 621-9 throu h contacts "of 'hi'indr'eds a bi,

register relays to one of the conductors 552, 553, etc. Assuming conductor to be thus grounded then a circuit is completed, comprising contacts of relay 803, to cause the operation of relay 80%. At this time also the record of the units digit on register 510 causes battery to be applied to either conductor or conductor depending on whether the units digit is even or odd. As suming the units digit to be even, then battery is connected through the left outer contacts of relay 619, conductor 668, through contacts of the units register relays 510, to conductor 554, causing the operation of relay 805.

The setting of the tens register 520 causes ground to be connected. over conductor 607, through contacts of tons relays 5520 to one oi" the conductors 556, 557, etc., to be grounded. Assun'iing conductor 557 to be thus grounded, a circuit is completed for operating the vertical ma net 301. which is associated. With the vertical row of contacts 302 wherein is located the first trunk leading to the private branch exchange, namely, trunk 323. The circuit for energizing magnet 301 n'iay be traced from battery, through the Winding of said magnot, through the cross connection blocks 370, conductor 352, front-contacts of relay 805, contacts of relay S03, conductor 851 contacts of tens relays 520, to the grounded conductor 66?. The setting of the units register causes ground to be extended through the right contacts 055 relay 609, conductor 651, through relays of the units register 510, conductor 852, contacts of relay 803, conductor 85d, conductor 855, to bat tery through the Winding of horizontal group relay T02. Relay 702 is individual to the section 30st of switch 300 wherein appears the first trunk in the desired P. B. X. group. Similarly relay 703 may be individual to a succeeding section as section 305. The operation of relay 702 extends ground through the lowermost contacts thereof, over conductor 752, to battery through the winding of relay 015. Relay 615 at its right contacts provides a locking circuit for the testing relays 250.

It will be noted that relay 806 was operated when the marker ground control relay 619 was GIlQlglZQtl. The circuit for operating relay 806 may be traced from battery, through the winding thereof, contacts of relay 843, coi'iductor 052-, left contacts of relay 611, to ground at the contacts of relay 01.9, li ith vertical magnet e01 operated a circuit is now completed from ground, through the left contacts 01": relay 806, Winding of relay 807, conductor 653, lower innermost contacts otmagent 301, conductor to battery through the winding of relay 704. Both relays 704 and 807 operate in this circuit "Re ay- 807 e tend g ound closes a through its left contacts, thence through the outermost front contacts of relay 80G, conductor 654:, contacts of relay 701, conductor 753, through the frame connector 210, to battery tl'irough the winding of vertical Id magnet 209. The operation of magnet 209 in this circuit prepares the vertical row of contacts in which appear the selected group of trunks including trunk 2G1. lriagnet 209 extends ground through its lower "5 contacts, over conductor 654, through the Winding of relay 601, to battery at the contacts of relay (ill. The test horizontal magnot 306 which individual to section 30% in switch 300 is now ener ized over a circuit which may be traced from battery, through the right winding of magnet 300,. conductor 35%, contacts of relays and 701, conductor 7%, lower middle contacts of magnet 30E, conductor right middle contacts oi relay to ground at the: right back contact oi r lay 811.

It will be assumed that the first trunk of the l B. X. group is idle when in: net 306 operates. Magnet 306 in operating test cir Knit which includes the sleeve conductor or the P. B. X. trunk This circuit may be traced from battery, through the Winding of relay 605, conductor 655, contacts of relay 70L and 702, conductor 755, lower conductor of the test link, thence through contacts in row to the test conductor of trunk be Trunk 0.0a ing idle there exists no ground potential on the sleeve conductor thereof: and relay G05 remains normal. Magnet 30G in or csting also extends ground through its left c over conductor 350, contacts of relay conductor 35W, contacts of relay 201, ductor to battery through the ninth of relay 503. Belay G03 operates and clos an obvious energizing circuit for 00 Magnet 306 also extends the grounded, upper conductor of the test link through contacts in vertical row 30:2, through the connecting blocks 350, over conductor 351 to battery through the Winding of the clocking relay 815. Relay operates to mark the beginning of the P B. X. group for purposes to be explained hereinafter.

The structure of the switches 300 and $00 is such that the horizontallink circuits are divided into five groups, corre ouding to the digits 0 to st and 5 to 9, inclusive. 'lhus in switches 300 and 400 there e ten different horizontal gl'OilPS. (ion cqucntly by ni'eansof the connecting block 1'. "0, the test links of these groups may associa d with the blocking relays 812, 8Y3, 813:, et I any desired manner. It has been that section 304 of switch 300 is the to LL01 tion, thus the fourthblockin'g relay 8i? was operated as above described. The operation of relay ill-dis an indication to the translater that the fi st line o the BB, K. group is located in the fourth section of switch 300. The purpose of operating relay 815 will be described in detail hereinafter.

Relay 815 also completes a circuit from battery, through the winding of relay'809, thence through the upper front contact of relay 815, to ground as above traced. Relay 809 extends ground through its inner right front contact, over con-:iluctor 856, contacts of relay 701, conductor 656, to battery through the winding of relay 610. The operation of relay 610 in this circuit,-serves as an indication to the marker that the con nection to be extended to a private branch exchange. Relay 610 completes a circuit from battery through the winding of relay 607, inner back contacts of relay 608, inner front contacts of relay 610, back contacts of relay 605 to ground at contacts of relay 604k. Relay 607 immediately locks to ground at the armature of relay 619.

When relay 702 operates as above described, it associates the test conductors of the links in section 304 of switch .300 with the test relays 250. A three pointtest is now made to determine an idle link in switch 200, an idlelink in section 301 of switch 300, and an idle trunk interconnecting both these links. It will be assumed that link 263, trunk 261, and link 308 are simultaneously idle. A test circuit is now prepared from battery through the right winding of relay 202, right middle contacts of relay 206, through the frameconnector 210 to the test conductor of link 263. Link 263 being idle no ground potential exists thereon and the right winding of relay 202 remains deenergized. Another test circuit is prepared from ba tery through the left winding of relay 202, right inner back contacts of relay 206, through contacts of relays 201 and 208 to the sleeve conductor of trunk 261. Trunk 261 being idle, the left winding of relay 02 is not energized, consequently relay 202 remains normal. A third test circuit is completed from battery through the-winding of relay 20%, back contacts of relay 211, conductor 253, contacts of relays 701 and 702, conductor 756, to the test conductor of link 308. Link 303 being idle the test relay 20lremains normal. With relays 202 and 201 normal a circuit is completed from battery, through the winding of relay 206, leftback contacts of relay 202, conductor 657, front contacts ofrelay 606, to ground at theleft back contacts of relay 609. It will benoted that relay 606 was operated when relay 807 operated. This circuit may be traced from battery, through the winding of relay 606, conductor 658, contacts of relay 701, conductor 659, right inner front contacts of relay 806, to ground at the contacts of relay 807. The operation of relay 206 as described above identifies the Lselectionmt. l nks 5263 and. 308

as well as the selection 'of trunk 261. A. circult-1s now completed from battery through the windin of vertical ma -net 300 contacts of relay 7 0%, conductor 757 contacts of relays 208 and 201, conductor 254:, left outerfront contacts of relay 206, left back contacts of relay 202, to ground over conductor 657 as above described. Magnet 300 prepares the contacts of vertical row 311 and extends ground through its lower inner contacts, over conductor 358, through the left back contacts of relay 811, conductor S59, contacts of relay 201 conductor-661,

to battery through the winding of relay 602. Relay 206 111 operating closes an obvious energizing circuit for relay 211 which operates and disconnects the test relay 20st from the link 308 to prevent a false operation of relay 204 when the test conductor of link 308is subsequently grounded. Horizontal 210, right outer front contact of relay206,

conductor 663, contacts of'relays 601 and ground at the left contacts of relay 607. The circuit for operating horizontal magnet 312 may be traced from battery through the right winding of said magnet,-

over conductor 359, contacts of relays 702 and 701, conductor 75.9, left contacts of relay .211,.to ground over conductor 663. The operation of magnets 212 and 312 completes the connection between trunk 152 and trunk 261, and also between trunk 261 and the first P. B. X. trunk 323. In the manner described in detail in the application of 1V.

WV. Carpenter, referred to hereinbefore, the

sleeve conductor of trunk 261 is grounded when magnet 212 operates thus closing the previously described circuit for test relay 605. Relay 605 operates and completes a circuit from battery through the winding of release relay 612, right outer front contact of relay 607, front contacts of relay 605 to ground at the contacts of relay -l.

Relay 612 completes an obvious operating circuit for relay 611. In the manner described in detail in the application of W. 1V. Carpenter, Serial No. 703,362 already referred to, the operation of relay 611 brings about the release of the marker. Subsequently to the release of the marker, the translator, the connectors 210 and 260,

sender connector 560, sender 500 and sender -selector160 are released.

The release of the marker results in the release of vertical magnets2l5, 209, 309 and 301. The connection'through switch 200 is maintained -.by magnet 212 which is now locked in a circuit comprising both windings of this magnet, contacts of switch 200, and the grounded sleeve conductor of trunk 261. In sim lar manner connection lSQnfilllttlHlBtl branch exchange, and also the manner in 5 ago which the connection is disrupted at the termination of conversation.

Sequence of operations when the first trunk of the P. B. X. group is busy.

It will now be assumed that the first trunk one is busy when the test horizontal magnet 306 operates as hereinbeitorc described. In this case the sleeve conductor of trunk 323 is grounded and when magnet 306 is energized, the circuits already traced for relays 605 and827 are closed resulting in the operation of both of these relays. Relay 605 in operating opens. the operating circuitof rela-y607, so that when relay 610 operates-as described above, a'circuit is completed from battery through the right winding of relay 609, right outer contacts of relay 610, right outer back contacts of relay 607, front contacts of relay 605 to ground at the contacts oti relay 604. Relay 609 operates and immediately locks by means of a circuit completed through its left windingand looking contact to ground at the contacts of relay 619. It will be noted that relays 815 and 809 operate in the manner herembefore described. Relay 609 extends ground through its inner front contacts to operate relay 608. A circuit is thereupon completed from battery, through the winding of relay 811, contacts of relay 803, conductor 861, left contacts of relay 608 to ground at the contacts of relay 619. 'Relay 811 atits right inner contacts providesa locking circult for relays 809 and 815. In addition relay 811 by its operation indicates to the translator that the first P. B..X. trunk is busy. With relays 809 andSll operated ground is extended through the outermost front contacts of relay 811, left. outer contacts of relay 809, conductor 857 to battery through the windings of relay 705 and 707 in parallel. Re1ay705 is individual to a section of the desired P. B. X. trunk group, which section appears .in vertical row 302, While relay 707 is individual to the corresponding row 402 of switch 400 wherein appear the remaining trunks of the desired P. B. X. group. In similar manner relays 706 and 709 may be individual to the P. B. X. trunks of another group appearing in a different pair of vertical rows, such as rows 307 and 407. The P. B. X. line test relay 827 is now connected to the sleeve conductor of the firstP. B. X. trunk 323. This circuit may be traced from battery, through the winding of relay 827, conductor 858, contacts of relay 705, conductor 755, lower conductor of of the test link associated with section 304, thence to the grounded sleeve conductor of trunk 323 thus causing relay 827 to operate and lock to ground at the contacts of relay 811. It has already been mentioned that relay 815 indicates to the translator that the first trunk in the desired P. B. X. group appears in the fourth section of switch 300. It will be asumed that this trunk group comprises seven trunks, two of which have an appearance in sections 304 and 305 of switch 300 while the remaining five have an appearance in the five sections of switch 400. As yet there has been given to the translator no indication as to the size of th trunk group, or in what section of switch.

300 or switch 400 the last trunk appears. hen relay 609 operates as above described it opens the original operating circuit for vertical magnet 309 which releases. Relay 609 also opens the previously described circuit for group relay 702 which new releases and disassociates the test relays 250 from the links in section 304. The operation of relay 811 as above described also opens the energizing circuit of test horizontal magnet 306 which releases. The energizing circuits of relays 605 and 615 are also opened when relay 702 releases both of said relays retracting their armaturcs. Relay 615 upon releasing opens the locking circuit of those test relays 250 which had become energized as a result of the testing of the links in switches 200 and 300. A circuit may now be traced for operating vertical magnet 401 which controls the vertical row or" contacts 402 in which appear the remaining five trunks of the group including trunks 323, 322, 416, etc. This circuit is completed from battery through the winding of magnet 401, conductors 452, through connecting blocks 370, lowermost contacts of magnet 301, conductor 361, to ground at the right inner contacts of relay 811. It will be noted that when relay 809 operated a circuit was completed from ground through the left outer contact s of said relay, conductor 857, thence in parallel through the windings of relays 705 and 707.

It will be remembered that relays 807 and 704 operated when vertical magnet 301 was actuated. Similarly, the actuation of magnet 401 as described, causes relays 808 and 708 to operate. This circuit may be traced from ground at the left contacts of relay 806, thence through the Winding of relay 808, conductor 863, lower innermost contacts of magnet 401, conductor 453, to battery through the winding of relay 708. Circuits are now completed for operating the last two test horizontal magnets of switch 300 and the five test horizontal magnets associated with switch 400. The circuit for operating magnet 306 alone will be thc first tive will be assumed that trunks of the P. X. group. namely. the two trunks appearing in switch 300. are busy and the trunks appearing before the first. three swctions of switch 400, and that the sixth P. B. X. trunk, namely, the trunk 423 is idle. In order to preserve relative simplicity in the drawing, only the last two sections in each of the switches 300 and 400 are shown. lVith the required hori zontal magnets operated, the P. B. X. trunk testing relays 827, 828, etc. are connected to the lower or test conductors of the corresponding sections in switches 300 and 400. Accordingly, a circuit is completed from batterv through the winding of relay 827, thence bv means of conductor 858 through contacts of relay 705, conductor 755, con tacts in vertical row 302 to the grounded conductor of the busy trunk 323. Similar circuits exist for operating relays 828, 829, 830 and 881, which look to ground at the contacts of relay 811. Since trunk 423 is idle, however, the corresponding test relay 832 remains normal. It will be noted that when test magnet 412 operates a circu t is completed from battery through the winding of relay 821, conductor 7 62, through the connecting block 460, contacts 111 vertical row 402 to the grounded upper conductor of the test link associated with magnet 412. Relay 821 iinn'iediately looks through its winding and locking contacts, thence through the locking contacts of relay809 to groiind at the contacts of relay 811. Relay 82l upon operating opens the energizing circuits of all the test horizontal magnets which thereupon release. The operation of any of the relays 827, 828 as above described closes an obvious operating circuit for the relay 823. Relay 823 is designed to be slow in operating to permit the testing relays 824, 825, etc. to take their proper setting. lVhen relay 823 has completely attracted its armatures, a circuit is completed from ground through the contacts of relay 823, lower outer back contacts of relays 812, 813 and 814, lower outer front contacts 0t relay 815, upper front contacts of relay 827, lower inner back contacts of relay 816, upper front contacts of relay 828, lower inner back contacts of relay'817, upper measoe front contacts of relay 829, lower inner back contacts of relay 818, upper front contacts of relay 830, lower inner back contacts of relay 819, upper front contacts of relay 831, lower inner back contacts of relay 820, upper back contacts of relay 832, conductor 874 through the connecting block 880, conductor 875, to battery through the winding of group relay 711. Relay 711 is individual to the sect-ion 404 wherein the first idlc P. B. X. trunk appears. It will be noted that even though the succeeding P. B. X. trunk 416 may also be idle and the corresponding test relay 833 be normal, the start circuit is opened at the upper contacts of relay 832 and group relay 711 alone is encr gized. Relay 711 extends ground through its lowermost contacts over conductor 752 to battery through the winding of relay 615 which operates. Relay 711 also connects the test conductors of the links in section 404 with the marker test relays 250. A threepoint test is now made comprising links in switch 200, trunks in the group interconnecting switches 200 and 400 as well as the links in section 404. The manner of making this test and the manner in which the idle P. B. X. trunk 423 is seized by the operation 0t switches 200 and 400 has been described hereinbefore in detail. The manner in which the connection is disrupted after the terminationof conversation is similar to that described in detail in the application of 1V. W. Carpenter Serial No. 703,362, filed April 1, 1924. It will be noted that subsequent to the seizure-of the idle trunk 423 when the translator and marker release, the operating ground for maintaining vertical magnets 301 and 401 energized is removed and both these magnets release simultaneously.

In the foregoing description it has been chosen to illustrate the invention as applied to a P. B. X. trunk group which terminates in two final switches, but it will be apparent to any one skilled in the art that trunk groups appearing in more than two final switches may be employed.

\That is claimed is:

1. In combination, a group of trunks, selective switches in which said trunks appear, testing means norn'ially associable with a particular one of said trunks, and means for partially operating said switches to as sociate all of said trunks with said testing means.

2. In combination, a group 01" trunks, selective switches in which said trunks appear, testing means normally assoc-iable with a particular one of said trunks, means for pzirtially operating said switches to associate all of said trunks with said testing means to mark for selection an idle trunk. means eti'ective when said trunk has been marked for completely operating 'that switch alone in which said idle trunk appears.

In combination, a group of trunks, selective switches comprising groups of link circuits before which said trunks appear, testing means normally associable with a particular one of said trunks, and means effective if said particular trunk is busy for partially operating said switches to associate said testing means with all of said trunks.

at. In combination, selective switches comprising groups of link circuits, a group of trunks, each of said trunks appearing before a corresponding group of said link circuits, means for testing said link circr other testing means normally arstmable with a particular trunk in said group, means effective when said part cular trui is inacessible for partially operationsaid switches to associate said other testing means with all the trunks in said group to mark for selection an idle one thereof, and. means responsive to the marking of said idle trunk for associating said first mentioned testing means with the group of link circuits before which said idle trunk appears.

5. In combination, selective switches comprising groups of link circuits, a group of trunks each trunk appearing before a corresponding group of links, testing means for testing the condition of the links in said switches other testing means normally associable with a particular trunk in said group, means for operating one of said switches to seize said particular trunk, means effective when said particular trunk is inaccessible for partially operating another of said switches to associate said other testing means with the remainder of said trunks to mark for selection an idle one thereof, and means responsive to the marking of said idle trunk for associating said first mentioned testing means with the group of link circuits before which the marked idle trunk appears.

(3, In combination, selective switches, a group of trunks appearingin said switches, testing means associable in common with said switches, means for partially Opfiltttlllgl' one of said switches to test the condition of a particular one of said trunks, means effective in one condition of said particular trunk for completely operating said one of said switches to seize said trunk, and means effective in another condition of said trunk for associatin said testing means with the remainder of said trunks to mark for selection an idle one thereof.

7. In combinatiomselective switches comprising groups of link circuits, a group of trunks, each trunk appearing before a corresponding group of link circuits. means for marking for selection a particular one of for completely operating the switch in said trunks, testing means cults other testing means tive dependent upon the busy said particular trunk for opt: To switch to associate said other test with the remaining trunks of mid mark for selection an idle one o r, means effective when said trimk has l marked for associating said first mentioned testing means with the groin) of link circuits before which the n'iaix'ced ti'llllli a1 pears. A

S. In combination, select-ire comprising groups of link circmts, 7. up ct trunks, each trunk appearing be pro 1 correspending group of link circuits, in testing the condition of said link .i other means for testing the cond said trunks, means for partially o one of said switches to test the coudit a particular one of said trunks, n tive in one condition of said tri pletely operating said one of 7 march. to seize said trunk, means effect another condition of said trunk for partiall operating another of said switches to said other testing means with the rcn trunks of said group and to mark for tion an idle one thereof, means e active when said idle trunk has been marked for associating said first mentioned testin 't means with the group of link circuits lief which said idle trunk appears, and means which said idle trunk appears.

9. In combination, a first selective switch, a second selective switch each of said switches comprising groups of link circuits, a plurality of trunks interconnecting said first and said second switches, a group of trunks outgoing from said second switch, a common mechanism for controlling the operation of said first and said second switches, testing means in said mechanism, means for associating said testing means with links in said first and second switches and with said interconnecting trunks, other testing means for the trunks outgoing from said second switch, means for operating said. second switch to test the condition of a particular trunk in said group of outgoing trunks, means effective when said particular trunk is busy for disassociating said first mentioned means from the links in said second switch alone and for associating said other testing means with the remaining trunks in said outgoing group of trunks to mark for selection an idle one thereof, and means effective when said trunk has been marked for causing said controlling mechanism to operate said first and said second switches to complete a connection to said idle trunk.

10. In combination, a private branch exchange, selective switches, a group of trunks leading from said switches to said private branch exchange, one of said trunks bearing a numerical designation the remainder of said trunks bearing no numerica designation, means for operating one of said switches to seize said designated trunk, testing means normally associable withithe numerically designated} unk', means effective when said designated trunk is inaccessible for associating said testing means with all the non-designated trunks to mark for selection an idle one thereof, and means for operating the particular switch in which said idle trunk appei 11. In combination, a private branch 0:;- change, selective switches comprising groups of link circuits, a group of trunks, each trunk app airing before a corresponding group of link circuits, testing means for said link circuits, means for associating said testing means with a particular group of link circuits, other testing means for said group of trunks, means eti'ective dependent upon the condition of the trunk appearing before said particular group of link circuits for disassociating said first mentioned testing means from said group of link circuits and for associating said other testing means with all the trunks of said group to mark for selection an idle one tl1ereof,'means effective when said idle trunk has been marked for associating said first mentioned testing means, with the group of links before which said idle trunk appears, and

means for operating the switch in which said idle trunk appears to complete a conneetion between said idle trunk and an idle link in the corresponding group of links.

12. In combination, a selective switch comprising link circuits arranged in groups, a group of trunks, each trunk appearing before a corresponding group of link circuits, a test link for each of said groups of link circuits, means for operating one of said test links to cause a test to be made of a particular one of said trunks,'means effective when said particular trunk is busy for operating all the said test links to cause a test to be made of all the trunks in said group for the purpose of marking for selection an idle one thereof, and means effective when said trunk has been so marled for releasing all of said test links and for completely operating the switch in which said idle trunk appears to complete a connertion to said idle trunk. W

13. In combination, selective switches comprising groups of link circuits, a group of trunks each trunk appearing before a corresponding group of link circuits, test links for each ol said group of link circuits, means for partially operating one of said switches to test the condition of a particular one of said trunks, means effective when said trunk is busy for operating all of said test links to cause a test tohe made of all the trunks in said group and for partially operating another of said selective switches, and means effective when an 

